Rocket assisted projectile

ABSTRACT

An improved projectile suitable for use in artillery pieces, through preferably in the higher calibres, is disclosed wherein projectile range upon launching by the gun is considerably extended by means of a solid propellant rocket motor in combination therewith which is characterized by internal means for supporting the solid propellant. Ignition of the propellant produces propulsive gases. The motor is operated after exit from the gun barrel and extends the flight range of the projectile.

United States Patent Wall 1 Oct. 17, 11972 [54] ROCKET ASSISTEDPROJECTILE 3,176,615 4/1965 De Matthew ..l02/49.7 X I 2,994 359 8/1961Westbrook et al.....l02/103 X 21 .RhdH.WllHtll,Al. [7 1 memo a e a2,816,721 12/1957 Taylor ..60/253 x [73] Assignee: Thiokol ChemicalCorporation, 3,122,884 3/1964 Grover et al ..102/103 X Br' t 1, Pa.

0 FOREIGN PATENTS OR APPLICATIONS [22] Filed: Oct. 29, 1969 1,168,8034/1964 Germany ..102/49.3 [21] Appl. No.: 872,176

Primary Examiner-Robert F. Stahl 52 us. (:1. ..102/49.3, 60/255,102/102, Brennan 2 A A 7 "102/103 A A 511 1m. (:1 ..F42b 13/02 [57]ABSTRACT [58] Field of Search,....l02/34, 34.1, 49.3,49.7, 103; Animproved projectile suitable for use in artillery 60/355 R5 255 pieces,through preferably in the higher calibres, is disclosed whereinprojectile range upon launching by [56] References Gifted the gun isconsiderably extended by means of a solid propellant rocket motor incombination therewith UNITED STATES PATENTS which is characterized byinternal means for supporting the solid propellant. Ignition of thepropellant 2489953 11/1949 Bumgy produces propulsive gases. The motor isoperated 2941469 6/1960 Barn after exit from the gun barrel and extendsthe flight 3,108,433 10/1963 De Fries et al ..102/103 X range Oftheprojecma 2,773,448 12/1956 Jasse ..60/256 X 1,879,579 9/1932 Stolfa eta1 ..102/34 X 9 Claims, 3 Drawing Figures Fig.l

INVENTOR. Richard H. Wal/ PATENTEU 17 I973 3.698321 sumanrs Fig.2

INVENTOR. Richard H. Wa// ROCKET ASSISTED PROJECTILE BACKGROUND OF THEINVENTION Artisans in the field of rocket propelled missiles have formany years sought to combine the capability of the ordinary cannon, orartillery piece operating by means of an explosive charge for launchingprojectiles and the like, with the steady state propulsion efficiencyderived from the burning of a solid propellant in a rocket motor. Thesedevices, known as rocket assisted projectiles, or gun boosted rockets,and with which this invention is concerned, have not, up to now, provedentirely satisfactory nor performed in accordance with expectations.Many reasons have been advanced for this, not the least of which is thefailure to develop a propellant grain which can withstand theaccelerations experienced during the difficult launching, or boost phaseof the projectile flight, or to develop means to protect the grain.Success has heretofore been elusive most often in the past because ofpropellant grain cracking, or other, similar deleterious effects inducedby the high launching acceleration forces to which the propellant issubjected. It is of course quite obvious that the rocket motorpropellant would be subjected to very high linear, tangential and radialacceleration forces during the launch of the missile and due to thespinning thereof imparted by the lands or rifling grooves on the insidesurfaces of the barrel of the gun which fires the projectile.Accordingly the invention to be hereinafter described provides, by meansof an unique internal casing and propellant support therein, a workableand operable rocket assisted projectile, which can be safely launched bymeans of ordinary field artillery equipment.

SUMMARY OF THE INVENTION This invention relates to rocket motors; moreparticularly it relates to rocket motors adapted for attachment to a gunboosted, or launched projectile.

It is well known in the artillery art that the range of a gun used tofire projectiles, or other ammunition rounds, can be considerablyincreased by the use therein of a rocket motor to impart propulsiveforces thereto. Such a rocket motor is usually rigidly affixed to theprojectile and gas evolved from an ignited propellant provide augmentingpropulsion efficiency. Ignition of the rocket motor can be accomplishedafter leaving the gun barrel with a suitably designed ignition systemcontained within the casing, or ignition can be accomplished by means ofthe high temperature gases from the launching charge in the gun barrel.There are, however other problems in the attainment of an operativerocket motor for projectiles which do not find such easy solutions. Aprimary concern is the very high acceleration forces experienced by suchprojectiles when launched from a gun since unwanted and difficultproblems arise therefrom. With respect to the projectile and its warheadpay load, these problems are of relatively little concern since adequatesolutions have long been available. However, with respect to the rocketmotor, a different situation obtains. Motor casings of ample strengthhave long been available; however, many state-of-the-art propellants arenot so durable, hence in providing a rocket motor for augmenting thepropulsion of the projectile after launching by the gun, the artisanmust insure that a propellant grain is ineluded which is capable ofwithstanding the launching forces, so that upon ignition, smoothcombustion, and therefore propulsion is obtained. From the above andother considerations to be hereinafter referred to, it appears quiteobvious that a most critical component in a rocket assisted projectile,from the standpoint of satisfactory operation and performance, is thepropellant.

In its preferred embodiment the present invention sets forth a solutionto the problem above referred to in the form of composite propellantcomprised of an oxidizer and an elastomeric binder such as carboxylterminated polybutadiene in combination with a novel support means in acasing containing the propellant.

Accordingly, it is an object of this invention to pro vide a rocketmotor in combination with a gun launched projectile for augmentingpropulsion of the projectile after exit thereof from the launching gun.

It is another object of this invention to provide a device of thecharacter described which utilizes a solid propellant grain, containedand supported in the rocket motor casing, so as to successfully operateeven under the extreme acceleration forces to which it is subjectedduring the critical launch period.

A still further object of this invention is to provide a gun launched,or boosted projectile, adapted to be propelled after launching by asolid propellant rocket motor, said motor comprising a casing withinwhich the solid propellant grain is so supported, that it becomescapable of undergoing strenuous accelerations without harmful effect.

Still another object of this invention is to provide a solid propellantrocket motor of the character described which is adaptable to supplypost fire propulsion to a gun boosted projectile, wherein a tube,centrally positioned interiorly of the motor, and within a centralperforation in the solid propellant grain, supports the grain understress conditions during launch which would cause the grain to undergostrenuous deformation without such support.

With the above and other objects and advantages in mind as will becomeapparent to those skilled in the art to which the invention pertains,the present invention comprises a rocket motor adaptable for use with aprojectile fired from a gun. The motor includes a casing, an elastomericsolid propellant grain in the casing and a support means therewithin ofa generally hollow support tube. The tube communicates with the nozzleof the rocket and serves both to conduct the hot gases produced by thesolid propellant grain when ignited and to support the grain during thegun boosted phase of the projectile-motor flight. Therefore these andother objects will hereinafter become more readily apparent from thefollowing description taken with reference to the drawings, wherein likereference numerals refer to like parts throughout, and in which aredescribed the preferred and additional embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a view, partially insection, illustrating one embodiment of projectile incorporating arocket motor of the invention;

FIG. 2 is a view similar to FIG. 1 showing the invention in anotherembodiment illustrative of a propellant configuration suitable for onetype of burning, and;

FIG. 3 is a longitudinal sectional view of a portion of another andpreferred embodiment of the invention illustrating propellantdeformation, under linear (left side) and radial (right side)acceleration stresses and further illustrative of a propellantconfiguration suitable for another type of burning.

DETAILED DESCRIPTION OF THE INVENTION To achieve a more detailedunderstanding of one embodiment of the invention herein presented,reference can be had to FIG. 1. FIG. 1 shows a projectile 10, includingby attachment thereto, a rocket motor 1 1 and a warhead 12. Motor 11comprises a casing 13 of steel, or other suitable pressure vesselmaterial such as reinforced fiberglass, or a laminate thereof to obtaina structure capable of withstanding high internal pressures and externalforces. Positioned in casing 13 is a solid propellant charge 14comprised of, preferably, an inorganic oxidizer and an elastomericbinder such as carboxyl terminated polybutadiene. Propellant 14 is mixedand cast into a sleeve, or cartridge 15 made of a resin such as epoxy,phenolic or polyisoprene with an inorganic filler of glass particles,asbestos or titanium dioxide. A liner or insulator 24 of a carbon-filledrubbery material can be interposed between the surfaces of propellant 14and cartridge 15 to provide bonding, or inhibiting qualities if desired.The exact inhibiting and bonding materials employed in liner orinhibitor 24 relates to the type of burning desired; i.e., end,radial ora combination thereof, and each is contemplated within the scope of thepresent invention as will be shown hereinafter. In essence, however, theinvention is more properly concerned with a novel support means forpropellant 14 whereby state-of-the-art propellants can be utilizedsuccessfully in gun launch applications. As will also be more fullyexplained in what follows, the propellant grain 14 is selected andformulated to be capable of readily deforming within limits controlledby a support means without damage during the high acceleration phases ofprojectile flight. Propellant 14, as stated, can be cast in place incartridge 15, and after proper cure, the loaded cartridge can beinserted, i.e., cartridge loaded in casing 13. Cartridge 15 is formedwith a central tube 16, which provides support for propellant 14 andforms therein a central perforation 17. Support tube 16, as indicatedabove, serves as a support member for propellant 14 during the launch,or firing stages of projectile 10, and can be formed with sideperforations 18 (FIG. 3), which are advantageous in some radial burningoperations, or can be, as is usual, formed with solid walls, for reverseend burning operation. Inhibitor 24 is bonded to the surfaces of centralperforation 17 but not to the outer surfaces of tube 16 for thefollowing reasons:

a. Propellant 14, during environmental storage over varying temperatureranges is permitted to expand and contract;

b. Ignition of propellant 14 along the surface of central perforation 17is prevented when used in end burning applications (cigarette fashion),by insulating against contact thereof with (hot) tube 16, or the hotrocket propellant gases that would fill the annular volume therebetween,said volume being that formed when propellant 14 is radially deformed,i.e., displaced from central tube 16 under the influence of high radialacceleration during axial spinning of projectile 111 and motor 11.

Fropellant 14 burning on the end surfaces only is shown by dashline A inFIG. 1. The arrows in FIG. 1 indicated the direction of flow of hot gasproduced by combustion of propellant 14, initiated in-flight by suitablemeans such as generally designated delay means 19 and igniter 20. Anozzle 21, aft mounted in casing 1 1 is aligned with tube 16 andprovides a means for exhausting gases generated by burning propellant 14to provide post launch propulsion to projectile 10. A plug 22 in nozzle21 prevents explosion gases produced upon firing of the gun fromentering the hot gas chamber defined by tube 16, and thereby causingpremature ignition of propellant 14.

It is sometimes desired, however, as indicated previously, to utilizethe heat of the launching charge gases for ignition of propellant 14.Accordingly a removable orifice plug 22-a provided in nozzle plug 22which is easily and rapidly dislodged during launch of projectile 10,after which hot gases flow through the orifice 22-h thereat, throughtube 16 and ignite propellant 14. Thus it is possible to effectsignificant weight savings and economies in projectile 10 by use of suchmeans as above described, since delay mechanism 19 and igniter 211 canbe entirely eliminated.

Referring now to FIG. 2, there is shown an end burning configuration ofpropellant grain 14 in casing 13. However, in this embodiment cartridgeor sleeve 15 is omitted and tube 16 is a recess or cavity 23 in casing11 by adhesive, or other well known means. To insure end burningoperation of propellant 14, insulative material or inhibitor 24 isapplied on all surfaces, as shown, except the head end surface so thatupon initiation of ignitor 211, burning occurs as in FIG. 1 embodiment,and as further indicated by the dash line B in FIG. 2. The arrows againillustrate the direction of hot gas flow, and show the reverse flow endburning aspect of propellant 14.

In FIGS. 1 and 2, at the lower portions thereof, casing 13 is providedwith a rotation band 25 which engages with lands in the gun barrel toeffect spinning of projectile 111 as it passes through the bore thereof.Thus it is readily apparent that during launch, very great accelerationsin the longitudinal direction are imparted which diminish rapidly tosome small negative value because of aerodynamic drag when projectile 10leaves the gun barrel. However, while projectile 10 at this time isundergoing no, or minimal linear acceleration, it is still subject tohigh radial accelerations, and propellant 14 will, in general, deform asindicated in FIG. 2 by dash line C, due to said high radial accelerationand the forces attendent therewith. Thus the end portions of propellant14 will be compressed during this period and will tend to move upwardtoward the insulated head end wall 27, and the surfaces of perforation17 away from tube 16 to provide therewith a generally annular volume orgap 28, which is wider at the head end and narrower in the aft endregions.

Referring now to FIG. 3 there is shown an additional and preferredembodiment of the invention wherein propellant 14 and tube 16 arearranged for radial ignition and subsequent burning thereof.

Grain 14, as shown in FIG. 3 is configured for radial burning, utilizingcentral tube 16 as in the reverse endburner configuration of FIGS. 1 and2. The major differences in grain 14 for radial burning and forendburning are in the location and thicknesses of inhibitors orinsulation. A critical feature of the radial burner is the provision ofgap or annular space 28 between propellant grain 14 perforation 1'7inner diameter and central tube 16 outside diameter at the time ofignition. Gap 28 can be closed under some conditions of tem peraturecycling and normal storage, but when projectile and motor 11 arespinning in operation, there must be provided sufficient free volume(end-play or air space) to allow gap 28 to form. On the other hand, afree volume (in the end of the motor) should be provided only to theextent necessary to form an ignition gap, since too much free volumethereat permits excessive strain in propellant 14 during spinning,causing cracks to form in grain 14. It has been found in most instancesthat confining gap 28 to a rage of 0.05 to 0.10 inch is ample forignition to take place in a satisfactory manner.

It is usually not necessary to provide radially burning grain 14 withother than a rather thin layer of inhibitor or insulation because inthis configuration burn time is short, hence motor casing 13 is exposedto high heat for a only short time. The inhibitor or liner must bebonded to propellant 14 but it is not necessary, or in some cases evendesirable, for it to be bonded to the case. Thus, propellant 14 can becast into a separate mold and then installed into the motor 11, or itcan be cast-in-place therein.

A layer of inhibitor or elastomeric material 29 can be applied to bothends of propellant 14- so that burning takes place primarily on theinside surfaces of perforation 17 and the length remains constant. Sinceinhibited propellant 14 is almost entirely an internally burningcylinder, a graph of chamber pressure plotted against burning time willshow a highly progressive trace or curve, maximum pressure being reachedat, or near burn-out.

Because of the progressivity of the pressure-time curve or trace, andthe high ratio of maximum to average pressure that would normally beencountered with radial burning configuration of grain 14, an ablativethroat insert can be advantageously used in nozzle 21. This can be amolded phenolic resin filled with asbestos, rather than an erosionresistant graphite as usually used in the end-burner configuration. Wlthan ablative or eroding throat, the throat increases in diameter assurface area increases. This permits operation of the motor 11 at ahigher average pressure, thereby achieving higher rocket-projectileperformance.

While components utilized with radial burner grain 14, such as motorcase 13, central tube 16, nozzle closure 22, igniter initiator 19 etc.,are the same as those for end burner configuration of FIG. 1 and FIG. 2,igniter 20 for the former is selected to be larger is size because thethroat area of nozzle 21 and propellant 14 surface area are larger;however in principle both operate similarly.

In operation, referring to FIG. 3, dash line E is representative of modeof deformation suffered by propellant 14 under linear, or longitudinalacceleration conditions. It is readily seen that a compressive forcecauses head end surface 2) to move downwardly away from insulating wall27-A, and also gap 28 is at least in part occupied by deformedpropellant 14. As spin rate increases, propellant M responds bydeforming as shown by dash line F in the right hand of FIG. 3. In thisposition it is longitudinally elongated until surface 29 abuts theunderside of insulated wall 27A, such that continued generation ofcentrifugal force, will cause compression of the now elongatedpropellant 14. Further, a larger portion of core perforation 17 is nowexposed and ignition along the surface thereof more easily occurs. Sincean inhibitor of sufficient thickness has been applied to surface 27burning will continue in core 17 in a radial direction therealong.Burning as noted above will be rapid because of the larger burningsurfaces, and burn time foreshortened.

Having described the invention and its several embodiments, it isobvious that other embodiments and uses of this invention will occur toskilled persons. Accordingly what has been described as an invention andfor which Letters Patent therefor is desired is set forth in thefollowing claims.

What is claimed is:

1. A rocket motor assisted projectile, said motor and projectilelaunched by a gun the in-flight propulsion means for which is saidrocket motor, said motor consisting of a propellant grain having acentral perforation and a casing, the inner surface of said casingdefining a propellant chamber, said casing terminating at its rear endin at least one nozzle; a supporting tube for said propellant grain,said tube forming the inner wall for said propellant chamber and beingconnected to said chamber through at least one opening, said grainconsisting of a solid propellant having an ultimate strain adapted towithstand relatively high axial and tangential forces when supported bysaid tube, said supporting tube extending into the central perforationof said grain and having an outer dimension which in a substantialnumber of cross sections thereof is less than the dimension of thecentral perforation in said grain, so that the grain during the launchof said projectile from said gun is forced to take support against saidtube without cracking, but so that when said axial force ceases saidgrain returns to its earlier shape and then elongates due to centrifugalforce to expose a space between the grain and the supporting tubewhereby at least radial burning is rendered possible.

2. A rocket assisted projectile according to claim 1 wherein the lengthof the grain is shorter than the length of the rocket chamber, such thata space is formed between the front end of the motor and the front ofthe grain, so that the grain after launch of said projectile and motor,is elongated by centrifugal forces until until contained by the oppositeends of said rocket chamber, and the space between said grain and saidsupporting tube becomes larger.

3. A rocket assisted projectile according to claim 1 wherein said grainis at least partially bonded to said inner surface of said casing.

4. A rocket assisted projectile according to claim 1 wherein the spacebetween the supporting tube and the grain is substantially uniform.

5. A rocket assisted projectile according to claim 1 further including anozzle plug for preventing hot gas from said launching gun charge fromentering the interior of said propellant chamber.

8. A rocket assisted projectile according to claim 1 wherein the tubematerial is selected from the group consisting of aluminum, magnesiumand alloys thereof.

9. A rocket assisted projectile according to claim 1 wherein thicknessof the supporting tube walls is substantially uniform.

1. A rocket motor assisted projectile, said motor and projectilelaunched by a gun the in-flight propulsion means for which is saidrocket motor, said motor consisting of a propellant grain having acentral perforation and a casing, the inner surface of said casingdefining a propellant chamber, said casing terminating at its rear endin at least one nozzle; a supporting tube for said propellant grain,said tube forming the inner wall for said propellant chamber and beingconnected to said chamber through at least one opening, said grainconsisting of a solid propellant having an ultimate strain adapted towithstand relatively high axial and tangential forces when supported bysaid tube, said supporting tube extending into the central perforationof said grain and having an outer dimension which in a substantialnUmber of cross sections thereof is less than the dimension of thecentral perforation in said grain, so that the grain during the launchof said projectile from said gun is forced to take support against saidtube without cracking, but so that when said axial force ceases saidgrain returns to its earlier shape and then elongates due to centrifugalforce to expose a space between the grain and the supporting tubewhereby at least radial burning is rendered possible.
 2. A rocketassisted projectile according to claim 1 wherein the length of the grainis shorter than the length of the rocket chamber, such that a space isformed between the front end of the motor and the front of the grain, sothat the grain after launch of said projectile and motor, is elongatedby centrifugal forces until until contained by the opposite ends of saidrocket chamber, and the space between said grain and said supportingtube becomes larger.
 3. A rocket assisted projectile according to claim1 wherein said grain is at least partially bonded to said inner surfaceof said casing.
 4. A rocket assisted projectile according to claim 1wherein the space between the supporting tube and the grain issubstantially uniform.
 5. A rocket assisted projectile according toclaim 1 further including a nozzle plug for preventing hot gas from saidlaunching gun charge from entering the interior of said propellantchamber.
 6. A rocket assisted projectile according to claim 5 whereinsaid plug has a closed orifice and said orifice is adapted to be openedby said gas from said launching gun charge, whereby said gas enters saidchamber and ignites said propellant grain.
 7. A rocket assistedprojectile according to claim 1 wherein the material of the supportingtube is ablatable by the gases produced by said solid propellant grain.8. A rocket assisted projectile according to claim 1 wherein the tubematerial is selected from the group consisting of aluminum, magnesiumand alloys thereof.
 9. A rocket assisted projectile according to claim 1wherein thickness of the supporting tube walls is substantially uniform.